Voltage regulators, such as DC-to-DC voltage converters, are used to provide stable voltage sources for various electronic systems. Efficient DC-to-DC converters are particularly needed for battery management in low power devices (e.g., laptop notebooks, cellular phones, etc.). A switching voltage regulator generates an output voltage by converting an input DC voltage into a high frequency voltage, and then filtering the high frequency input voltage to generate the output DC voltage. Specifically, the switching regulator includes a switch for alternately coupling and decoupling an input DC voltage source (e.g., a battery) to a load (e.g., an integrated circuit (IC)). An output filter, typically including an inductor and a capacitor, may be coupled between the input voltage source and the load to filter the output of the switch, and thus provide the output DC voltage. A controller (e.g., a pulse width modulator, a pulse frequency modulator, etc.) can control the switch to maintain a substantially constant output DC voltage.
Lateral double-diffused metal oxide semiconductor (LDMOS) transistors are commonly used as a power switch in switching regulators due to their performance in terms of a tradeoff between their specific on-resistance (Rdson) and drain-to-source breakdown voltage (BVds), while CMOS transistors are widely used for controller and driver design. Semiconductor manufacturing processes that integrate both LDMOS transistors and CMOS transistors on a same piece of silicon, such as in a Bipolar-CMOS-DMOS (BCD) process, enables monolithic integration of switching regulators, including power switches, drivers and controllers, resulting in higher performance.
Drain and body region formation and optimization are key process steps used in making LDMOS transistors. In conventional approaches to fabricating LDMOS transistors, either the drain and body regions do not share process steps with CMOS transistors, thus increasing an overall number of BCD process steps and associated manufacturing cost, or the optimization of the drain and body regions includes a thermal cycle that can interrupt an existing CMOS process flow, thus increasing the BCD process integration complexity.